The present invention relates generally to batteries and electrochemical cells, and relates more specifically to an air mover system with a synthetic air jet for metal-air electrochemical cells.
Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power.
Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical xe2x80x9cbutton cellxe2x80x9d was not practical because it would lead to premature failure as a result of flooding or drying out.
In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983 and 5,356,729. An example of an advanced system for isolating a metal-air cell is U.S. Pat. No. 5,691,074.
A disadvantage of most air managers, however, is that they utilize an air moving device, typically a fan or an air pump, that occupies space that could otherwise be used for battery chemistry to prolong the life of the battery. This loss of space presents a particular challenge in attempts to provide a practical metal-air cell in small enclosures such as the xe2x80x9cAAxe2x80x9d cylindrical size now used as a standard in many electronic devices.
In addition to being bulky, air moving devices used in metal-air batteries also consume energy stored in the metal-air cells that might otherwise be delivered as power output to a load. Complicated electronics for controlling an air manager can increase this use of stored energy. Also, as most air moving devices used in metal-air cells distribute air to a cathode plenum at low pressure, a flow path must be defined passing over all regions of the cathode surface to evenly distribute air to the entire cathode surface. Thus, the function of bringing in make up air and the function of mixing and distributing air within the battery have been separate. A further disadvantage of fans used as air moving devices in metal-air cells is that they may create noise at a level disruptive to users of devices such as cellular telephones.
As a result, while a key advantage of metal-air cells is their high energy density resulting from the low weight of the air electrode, this advantage is compromised by the space and power required for an effective air manager, and the noise it may produce.
Therefore, there has been a need in the art for an air manager incorporating an air moving device that occupies less of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal-air cell, is quiet, does not require a complex baffle system in the cathode air plenum to distribute the air, needs relatively simple controls, and consumes power at a relatively low rate.
The present invention seeks to solves the problems described above. The present invention seeks to provide an air moving device that occupies less volume than conventional air movers, is usable with advanced systems for isolating air electrodes, does not require a complex baffle system for distributing air throughout the cathode air plenum, is quiet, and needs relatively simple controls, and consumes power at a relatively low rate.
These objects are accomplished according to the present invention in an air manager for a metal-air battery, comprising a synthetic air jet and a metal-air cell in a battery casing. The battery casing has an inlet and an outlet to permit air to flow into and out of the casing. The synthetic air jet has a housing with an internal cavity, and an opening into the housing to permit air to flow into the housing and to flow out of the housing. A movable member changes the internal volume of the synthetic air jet housing allowing ambient air to enter the inlet into the battery casing, and enter through the opening into the synthetic jet housing. The air is then expelled through the opening out of the housing into the casing, and at least some of the air escapes out of the casing through the outlet to the ambient air outside the casing. Along its path, the air passes adjacent to an air electrode of the metal-air cell.
In one preferred embodiment, diffusion isolation tubes extending either inside or outside the battery casing can connect to the casing inlet and the casing outlet to help regulate the air flow and the moisture exposure of the metal-air cell.
The movable member can be a flexible diaphragm incorporated into the housing of the synthetic air jet. The flexible diaphragm can be made from metal or can incorporate metal. Then the internal volume of the synthetic air jet can be varied with an electrode activated to attract and/or repel the diaphragm. Control of the air flow through the battery casing is regulated by controlling the rate of change of the internal volume of the synthetic air jet.
In another embodiment, a piston can be incorporated into the housing of a synthetic air jet to change the internal volume of the synthetic air jet using any conventional drive mechanism for actuating a piston.
More particularly describing a preferred embodiment, a synthetic air mover for a metal-air battery comprises a casing with an inlet and an outlet. A metal-air cell comprising an anode and a cathode are also located within the casing. A synthetic air jet located inside the casing draws air from outside the casing through the inlet. The air passes through the inlet into the casing and across the cathode. The air is then expelled by the synthetic air jet through the outlet out of the casing. A means for activating the synthetic air jet controls and regulates the air flow through the battery casing. Diffusion isolation tubes extending either inside or outside the battery casing can connect to the casing inlet and the casing outlet to help regulate the air flow and the moisture exposure of the metal-air cell.
In yet another aspect of the invention, a synthetic air jet for a metal-air battery can be positioned inside different sized casings, such as prismatic or cylindrical casings. In any sized casing, the synthetic air jet should admit sufficient quantities of air into the casing to supply an air electrode of the metal-air battery.
Other objects, features, and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the drawings and the appended claims.